Production of hemp protein isolate-polyphenol conjugates through ultrasound and alkali treatment methods and their characterization

Two easy-to-implement methods, i.e., ultrasound and alkali treatment, were used to produce conjugates of hemp protein isolate (HPI) and polyphenols (gallic acid and catechin). The effect of these two methods of conjugation on the degree of conjugation (free amino and sulfhydryl group contents), particle size, charge tensity, secondary and tertiary structures, surface hydrophobicity, solubility and emulsifying properties, antioxidant activities of the resulting conjugates were determined. The effect of conjugation on the storage, temperature, and salt sta-bility was evaluated. The results showed that alkali treatment induced more polyphenols to conjugate with HPI than ultrasound treatment. The conjugation significantly improved the solubility, emulsifying properties of HPI, especially in the case of HPI-gallic acid conjugate prepared through ultrasound treatment. The improvement in technofunctional properties correlated with unfolding of molecules, reduced particle size, surface hydrophobicity, interfacial tension, and increased charge intensity. The conjugation of HPI with polyphenols improved its antiox-idant activities. Emulsions stabilized by conjugates also exhibited higher storage, temperature and salt stability. These findings indicate that these two easy-to-implement conjugation methods can be readily used to develop HPI-polyphenol conjugates and use them as new class of emulsifier.